1. Field of the Invention
The present invention relates to hand portable chain saws, and more particularly to a safety device for such chain saws which is operable to prevent the risk of operator injury which may be caused by the cutting chain when the operator was subjected to a sudden movement of the chain saw, as in the case of "kickback", or when the operator's hand slipped from the front hand grip of the saw toward the cutting chain.
2. Description of the Prior Art
It is known that hand portable chain saws are subject to a so called kickback motion during a cutting operation, since the cutting chain may often engage a solid object such as a branch at the tip of the guide bar thereby causing an abrupt upward movement of the chain saw. This abrupt action of the chain saw may cause the moving cutting chain to come into contact with the operator's body thereby resulting in serious injury. Further, when the operator, in attempting to perform an untoward cutting operation, is using a downward force to the grip, or by reason of inadvertency, his hand may slip from the hand grip of the saw into contact with the cutting chain.
The prior art has proposed various safety devices for preventing the above-noted unexpected accidents in connection with chain saws. Such a safety device is known from the U.S. Pat. No. 3,776,331 issued to Lennart Gustafsson, wherein a trigger means (a safety brake lever) serves to release a locking mechanism and apply a spring force to a brake band around the drum for driving the cutting chain, thereby arresting the rotational movement of the drum in the event of a kickback. However, this device is rather complicated, incorporating an intermediate lever and other elements in the braking mechanism extending from the trigger means to the brake band. Thus, in this device the transmission of braking force is indirect and complicated, there being possible delay in actual braking time.